1. Field of the Invention
The present invention relates to a wireless communication system consisting of a wireless communication apparatus and a wireless communication control apparatus.
2. Related Background Art
In a wireless communication system such as a PHS (Personal Handy Phone System), while a wireless communication terminal apparatus is on standby in a wireless base station of its own system, it may be out of an area of the wireless base station due to its movement. In order to cope with the wireless communication terminal apparatus being out of an area due to its movement, various management processing technologies have been proposed (e.g., Japanese Patent Application Laid-open Nos. 9-218253 and 8-294165).
In addition, in a case where various wireless communication systems mixedly exist in a floor where OA apparatuses are installed, for example, a plurality of wireless base stations exist in extensions of a PXB (Private Branch Exchange), a collision occurs between control signals transmitted by the wireless base stations, with the result that a wireless communication terminal apparatus on standby and its wireless base station become out of synchronization.
Thus, if a situation arose in which a wireless communication terminal apparatus was not able to receive a call in when there actually was the call in, it is unclear whether this was due to a failure of the wireless communication terminal apparatus or because the wireless communication terminal apparatus was out of synchronization and happened to fail to receive the call in, which results in a problem.
FIG. 1 illustrates a configuration of a conventional wireless communication system. Out of synchronization at the time of processing standby in the conventional art will be described with reference to this figure.
In FIG. 1, reference numeral 900 denotes a management unit (management apparatus) that is connected to wireless base stations 902a, 902b and 902c, which cover networks (A) 901a, (B) 901b and (C) 901c, respectively, as its area. Reference numeral 903 denotes a wireless communication terminal apparatus connected to an OA apparatus 909. In addition, the management unit 900 is connected to a management center 907 via a public network 906 and can be operated and maintained remotely from a host computer 908.
Reference numeral 904 denotes a Private Branch Exchange (PBX) in which PBX wireless base stations 905a, 905b, 905c and 905d exist. In addition, it is assumed that the wireless communication terminal apparatus 903 is currently on standby in the wireless base station 902a. 
Next, processing of out of standby in the conventional wireless communication system consisting of the above-mentioned configuration will be described with reference to a sequence chart of FIG. 2.
The wireless communication terminal apparatus 903 is currently on standby in the wireless base station 902a (S1000). Although the OA apparatus 909 which is a maintenance object apparatus is fixedly installed, notification signals that are steadily transmitted among the wireless base station 902a on standby and the other wireless base stations collide with each other, whereby synchronization of standby becomes out of order (S1001). The wireless communication terminal apparatus 903 transmits a control channel release display indicating that synchronization is out of order to the main OA apparatus 909 (S1002). Upon receiving it, the OA apparatus 909 transmits a control channel establishment request for causing the wireless communication terminal apparatus 903 and the wireless base station 902a to take synchronization again (S1003) and establishes resynchronization of standby (S1006).
If there is a call in from the management center 907 until the resynchronization of standby is established (S1004, S1005), since the wireless communication terminal apparatus 903 is out of synchronization, it cannot respond to the call in.
Further, in FIG. 2, step S1007 indicates a control channel establish display to be transmitted from the wireless communication terminal apparatus 903 to the OA apparatus 909, step S1008 indicates a call in NG to be transmitted from the wireless base station 902a to the management center host 908 and step S1009 indicates standby.
However, according to the above-mentioned conventional art, it is unclear whether the wireless communication terminal apparatus 903 was out of synchronization of standby with the wireless base station 902a that is performing a standby operation or failed due to a trouble. Moreover, depending on an environment in which a wireless communication system is installed (a situation in which a plurality of wireless base stations exist and collisions among wireless state notification signals occur frequently), out of synchronization of standby occurs frequently and a wireless communication terminal apparatus cannot easily respond to a call in, whereby a possibility of loss of the call in increases.